US4270997A - Laser photochemical synthesis of Si3 N4 - Google Patents

Laser photochemical synthesis of Si3 N4 Download PDF

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Publication number
US4270997A
US4270997A US06/137,887 US13788780A US4270997A US 4270997 A US4270997 A US 4270997A US 13788780 A US13788780 A US 13788780A US 4270997 A US4270997 A US 4270997A
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United States
Prior art keywords
laser
controlled atmosphere
reaction chamber
gases
fiber
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US06/137,887
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James A. Merritt
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US Department of Army
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US Department of Army
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Priority claimed from US06/087,115 external-priority patent/US4227907A/en
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    • CCHEMISTRY; METALLURGY
    • C03GLASS; MINERAL OR SLAG WOOL
    • C03CCHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
    • C03C25/00Surface treatment of fibres or filaments made from glass, minerals or slags
    • C03C25/10Coating
    • C03C25/42Coatings containing inorganic materials
    • CCHEMISTRY; METALLURGY
    • C01INORGANIC CHEMISTRY
    • C01BNON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B21/00Nitrogen; Compounds thereof
    • C01B21/06Binary compounds of nitrogen with metals, with silicon, or with boron, or with carbon, i.e. nitrides; Compounds of nitrogen with more than one metal, silicon or boron
    • C01B21/068Binary compounds of nitrogen with metals, with silicon, or with boron, or with carbon, i.e. nitrides; Compounds of nitrogen with more than one metal, silicon or boron with silicon
    • CCHEMISTRY; METALLURGY
    • C03GLASS; MINERAL OR SLAG WOOL
    • C03CCHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
    • C03C25/00Surface treatment of fibres or filaments made from glass, minerals or slags
    • C03C25/10Coating
    • C03C25/12General methods of coating; Devices therefor
    • C03C25/22Deposition from the vapour phase

Definitions

  • optical fibers in excess of 2 ⁇ 10 5 psi is a desirable feature for certain specialized application (e.g., optical waveguides employing lengths of fiber).
  • Silicon nitride (Si 3 N 4 ) is an appropriate coating since it is resistant to moisture penetration and bonds securely to the silicon substrate fiber. Previous attemps to clad silicon fibers with Si 3 N 4 uses thermal (pyrolysis) techniques.
  • LPR laser photochemical reactions
  • An object of this invention to provide a method of coating optical fibers with Si 3 N 4 produced by laser photochemical reactions.
  • Another object of this invention is to deposit Si 3 N 4 on freshly-drawn silicon optical fibers in an atmospheric controlled chamber in a continuous operation which employs SiF 4 and NH 3 as the reaction gases.
  • a further object of this invention is to deposit Si 3 N 4 on freshly-drawn silicon optical fibers in an atmospheric controlled chamber in a continuous operation which employs SiH 4 and NF 3 as the reaction gases.
  • Si 3 N 4 is produced at room temperature in an atmospheric controlled chamber are coated with Si 3 N 4 by laser photochemical reactions which are initiated in accordance with the following equation: ##EQU1## wherein X is H and/or F when reaction is initiated by a CO 2 laser.
  • a silicon optical fiber is hermetically sealed by cladding with Si 3 N 4 synthesized by laser photochemical reactions initiated on the gases SiX 4 and NX 3 in a controlled atmosphere.
  • the silicon optical fiber is prepared in a standard fiber drawing furnace from a preform rod of fused silica which is brought to its yield point at about 2000° C.
  • the silicon fiber is drawn from the preform and through a chamber with controlled atmosphere (SiX 4 and NX 3 gases, wherein X is hydrogen and/or fluorine) at room temperature.
  • the laser is used to irradiate this atmosphere to form Si 3 N 4 which is coated on the silicon optical fiber to a thickness of about 0.02-0.20 micrometer.
  • the laser photochemical reaction initiated by the process of this invention when conducted in the presence of other substrates; e.g., other than optical fibers such as rocket motor nozzles or other components is effective in providing a coating of Si 3 N 4 on the substrates at room temperature (about 25° C.).
  • This method permits coating other materials which could not withstand high temperature conditions employed by vapor deposition method.
  • a pressure between about 10 and 200 torr of the reactive gases is satisfactory for coating the silicon optical fiber with the reaction product, Si 3 N 4 .
  • the thickness of the coating is proportionate to the flow rate of the reactants through the reaction chamber.
  • the laser photochemical reaction initiated by the process of this invention is an effective method for producing the compound Si 3 N 4 at room temperature.
  • the laser photochemical synthesis can be carried out by employing a pulsed laser or a continuous wave laser.
  • the laser radiation is directed through a salt window into a controlled atmosphere of SiX 4 and NX 3 , wherein X is selected from hydrogen and/or fluorine.
  • Si 3 N 4 is synthesized from SiF 4 +NH 3 and/or SiH 4 +NF 3 at room temperature in either a batch process or in a continuous flowing process.
  • the product is separated as a solid powder in high yield by using a cold finger or scraping the solid powder from reaction chamber surfaces.
  • the laser photochemical synthesis is illustrated as follows: ##EQU2##

Abstract

Disclosed is a method to synthesize Si3 N4 from SiX4 +NX.s3, wherein X is selected from hydrogen and/or fluorine, by laser photochemical reaction (LPR) technique in a controlled atmosphere chamber wherein the reactant gases are maintained at pressures between about 10 and about 200 torr in a molar volume ratio of about 3 of the SiX4 to about 4 of the NX3. The LPR method produces the compound Si3 N4 at room temperature while employing a pulsed laser or a continuous wave laser.

Description

DEDICATORY CLAUSE
The invention described herein may be manufactured, used, and licensed by or for the Government for governmental purposes without the payment to me of any royalties thereon.
CROSS-REFERENCE TO RELATED APPLICATION
This is a division of application Ser. No. 087,115, filed Oct. 22, 1979, now U.S. Pat. No. 4,227,907.
BACKGROUND OF THE INVENTION
The mechanical strength of optical fibers in excess of 2×105 psi is a desirable feature for certain specialized application (e.g., optical waveguides employing lengths of fiber).
Lack of mechanical strength is due to submicron flaws in the surface attributed, mainly, to chemical attack by atmospheric contaminants (e.g., moisture) during and after fiber drawing. Attempts to solve these problems have been studied by applying organic coatings to the fiber following the drawing of the fiber. Failure resulted because those organic coatings are not impervious to moisture or hydroxyl penetration. The penetration by moisture or hydroxyl resulted in reduced strength of the coated fiber during periods of storage and/or use.
Silicon nitride (Si3 N4) is an appropriate coating since it is resistant to moisture penetration and bonds securely to the silicon substrate fiber. Previous attemps to clad silicon fibers with Si3 N4 uses thermal (pyrolysis) techniques.
Thermal (pyrolysis) methods of influencing chemical processes lead, mainly, to the excitation of all degrees of freedom of the molecule. Both external (translational) and internal (electronic, vibrational and rotational) degrees of freedom are usually in thermodynamic equilibrium. In addition to there being an unproductive waste of energy, reactions with equilibrium excited molecules characteristically proceed in the direction of breaking the weakest bond, have a considerable percent of back reaction, many side reactions, and produce polymers.
Advantageous would be a method which employs laser photochemical reactions (LPR) to produce silicon nitride to clad freshly-drawn silicon fibers in an atmospheric controlled chamber. A particular advantage is recognized over the prior art vapor deposition method since the LPR method can be effected at room temperature.
An object of this invention to provide a method of coating optical fibers with Si3 N4 produced by laser photochemical reactions.
Another object of this invention is to deposit Si3 N4 on freshly-drawn silicon optical fibers in an atmospheric controlled chamber in a continuous operation which employs SiF4 and NH3 as the reaction gases.
A further object of this invention is to deposit Si3 N4 on freshly-drawn silicon optical fibers in an atmospheric controlled chamber in a continuous operation which employs SiH4 and NF3 as the reaction gases.
SUMMARY OF THE INVENTION
Si3 N4 is produced at room temperature in an atmospheric controlled chamber are coated with Si3 N4 by laser photochemical reactions which are initiated in accordance with the following equation: ##EQU1## wherein X is H and/or F when reaction is initiated by a CO2 laser.
DESCRIPTION OF THE PREFERRED EMBODIMENT
A silicon optical fiber is hermetically sealed by cladding with Si3 N4 synthesized by laser photochemical reactions initiated on the gases SiX4 and NX3 in a controlled atmosphere.
The silicon optical fiber is prepared in a standard fiber drawing furnace from a preform rod of fused silica which is brought to its yield point at about 2000° C. The silicon fiber is drawn from the preform and through a chamber with controlled atmosphere (SiX4 and NX3 gases, wherein X is hydrogen and/or fluorine) at room temperature. The laser is used to irradiate this atmosphere to form Si3 N4 which is coated on the silicon optical fiber to a thickness of about 0.02-0.20 micrometer.
The laser photochemical reaction initiated by the process of this invention when conducted in the presence of other substrates; e.g., other than optical fibers such as rocket motor nozzles or other components is effective in providing a coating of Si3 N4 on the substrates at room temperature (about 25° C.). This method permits coating other materials which could not withstand high temperature conditions employed by vapor deposition method. A pressure between about 10 and 200 torr of the reactive gases is satisfactory for coating the silicon optical fiber with the reaction product, Si3 N4. The thickness of the coating is proportionate to the flow rate of the reactants through the reaction chamber.
The laser photochemical reaction initiated by the process of this invention is an effective method for producing the compound Si3 N4 at room temperature. For this particular method the laser photochemical synthesis can be carried out by employing a pulsed laser or a continuous wave laser. The laser radiation is directed through a salt window into a controlled atmosphere of SiX4 and NX3, wherein X is selected from hydrogen and/or fluorine. For example Si3 N4 is synthesized from SiF4 +NH3 and/or SiH4 +NF3 at room temperature in either a batch process or in a continuous flowing process. The product is separated as a solid powder in high yield by using a cold finger or scraping the solid powder from reaction chamber surfaces. The laser photochemical synthesis is illustrated as follows: ##EQU2##

Claims (1)

I claim:
1. A method of producing Si3 N4 by laser photochemical reaction initiated by irradiating the reactant gases in a controlled atmosphere laser reaction chamber, said method comprising: (a) introducing into a laser reaction chamber that is provided with a salt window transparent to laser radiation, a controlled atmosphere of the reactant gases of SiX4 and NX3, wherein X is selected from hydrogen and fluorine, said gases maintained in a controlled atmosphere at pressures between about 10 and about 200 torr in a molar volume ratio of about 3 of said SiX4 to about 4 of said NX3 ;
(b) irradiating said controlled atmosphere with the P(36) line of a CO2 laser to produce said Si3 N4 as a powdery solid; and,
(c) separating and removing said powdery solid of Si3 N4 from said laser reaction chamber.
US06/137,887 1979-10-22 1980-04-07 Laser photochemical synthesis of Si3 N4 Expired - Lifetime US4270997A (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
US06/137,887 US4270997A (en) 1979-10-22 1980-04-07 Laser photochemical synthesis of Si3 N4

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US06/087,115 US4227907A (en) 1979-10-22 1979-10-22 Laser photochemical synthesis coating of optical fiber
US06/137,887 US4270997A (en) 1979-10-22 1980-04-07 Laser photochemical synthesis of Si3 N4

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Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4568565A (en) * 1984-05-14 1986-02-04 Allied Corporation Light induced chemical vapor deposition of conductive titanium silicide films
US4617237A (en) * 1984-05-14 1986-10-14 Allied Corporation Production of conductive metal silicide films from ultrafine powders
US5425922A (en) * 1991-12-27 1995-06-20 Vicor Company Of Japan, Ltd. Apparatus for manufacturing microcrystal particles and manufacturing method for the microcrystal particles
US20060225534A1 (en) * 2004-10-13 2006-10-12 The Research Foundation Of State University Of New York Production of nickel nanoparticles from a nickel precursor via laser pyrolysis

Non-Patent Citations (2)

* Cited by examiner, † Cited by third party
Title
Brekel et al., Journal of Electrochemical Society (Mar. 1972), pp. 372-375. *
Gross, Optical Engineering (Nov./Dec. 1974), vol. 13, No. 6, pp. 506-508. *

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4568565A (en) * 1984-05-14 1986-02-04 Allied Corporation Light induced chemical vapor deposition of conductive titanium silicide films
US4617237A (en) * 1984-05-14 1986-10-14 Allied Corporation Production of conductive metal silicide films from ultrafine powders
US5425922A (en) * 1991-12-27 1995-06-20 Vicor Company Of Japan, Ltd. Apparatus for manufacturing microcrystal particles and manufacturing method for the microcrystal particles
US20060225534A1 (en) * 2004-10-13 2006-10-12 The Research Foundation Of State University Of New York Production of nickel nanoparticles from a nickel precursor via laser pyrolysis

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